Strobe units are often used as visual alarm indicating output devices in fire alarm systems. As is known, such units emit a high intensity light periodically, for example once a second, to provide an ongoing indication that an alarm condition has been detected somewhere in the region being monitored. One such unit has been disclosed in U.S. patent application Ser. No. 10/040,968 filed Jan. 2, 2002 for Processor Based Strobe with Feedback assigned to the Assignee hereof and incorporated by reference herein.
Known units include an energy storage device, for example one or more capacitors, coupled to a gas discharge tube. When the tube is triggered with an appropriate control signal it emits high intensity light while discharging the storage device.
Known strobe units exhibit maximum peak current values subsequent to discharge of the storage element when the tube is triggered. The peak or surge current is primarily due to the fact that electrolytic capacitors in the device need to be recharged for the next flash.
FIG. 1 illustrates a representative timing diagram of peak capacitor recharge current values IREP. These peak current values are of a type exhibited by known strobe units each time the gas filled tube is triggered. At startup, a substantially larger initial current surge I0, which might be as large as 10 amps is exhibited by known units. In contrast, the peak repeating current values IREP fall in a range of 5 to 7 amps. In contradistinction, the steady state IRMS current typically falls in range of 50 milliamps to 800 milliamps.
It is also known that the magnitudes of the peak initial current surge I0 as well as the repetitive peak current values IREP vary continuously, from one second to the next, in response to discharge characteristics of the capacitors, the form of electrical energy being supplied to the unit as well as the phase thereof.
In view of the fact that the initial peak current draw I0 as well as the repetitive peak current draw IREP are exhibited by each of the strobe devices in the system it would be desirable to be able to limit not only the initial peak current surge but also the repetitive ongoing current surges as the unit flashes. Preferably, limiting the amplitudes of the peak current surges can be done without affecting the ability of the units to recharge adequately during the available one-second period to provide the next flash of light. Additionally, it would be desirable if peak current limiting could be achieved without substantial increase in heat generated by the respective strobe units or without substantially increasing the size, cost or manufacturing complexity of such units.